Etching process



tions of it onto the metal. This is permitted UNITED STATES PATENT OFFICE.

our. G. oLsoN, or cmcnco, ILLINoIs, ASSIGNOR '10 ILLINOIS TOOL WORKS, or

CHICAGO, ILLINoIs, A CORPORATION or ILLINOIS.

ETCHING PROCESS.

No Drawing.

To all whom it may concern Be it known that I, CARL G. OLsoN, a citizen of the United States, residing atChicago, in the county of Cook and Stateof Illinois, have invented a certain new and useful Improvement in Etching Processes, of which the following is a specification.

y invention resides in a new and improved method of etching metallic surfaces, and the general object of the invention is to accomplish the etching in a rapid, economical and neat manner. Heretofore etching processes have included applying to the metallic surface a substance impervious or resistant to the etching fluid and the subsequent removal-of such substance. One of the specific objects of my invention is to provide a process by which the metallic surface may be etched without the need'of coating it in any manner.

According to my method the operator first takes a thin sheet of paper and coats it with a plastic substance resistant to the etching fluid. For. brevity this may be termed the '26 resistfand while it is possible to employ different substances for the purpose, including wax or waxy material, I prefer to employ asphaltum.

The operator then-makes an impression in the resist similar to the pattern which it is desired to reproduce on the metallic surface. The impression may be made manually or by means of astamp, but I have found "that for practical purposes a rubber stamp is desirable. According to the preferred method a piece of tissue paper, previously soaked in water, is placed over the 'asphaltum or resist while the same is still plastic and before it has had time to harden, and the impression is made by pressing the .stamp upon the tissue, the lines being made deep enough to expose the main sheet of paper. The asphaltum is forced out from under the lines of the stamp, the stamp thus acting through the wet tissue which may be readily removed after been made. v

Next, the coated and impressed sheet is placed-with its uncoated side in contact with the surface to be etched. The etching fluid is then applied to the coated side of the sheet and soaks through the exposed porthe impression has 7 'specification of Letters Patent. I Application flledlliay 27,

Patented Nov. 2, 1920. 1920. Serial N 384,597.

to continue for a half minute, or whatever period is found by experience to be best for the particular results desired, after which the sheet is simply removed and the surface washed with an alkali solution for neutralizing the acid remaining on the metal. While the exact composition of the etching fluid is not essential and should be varied for dif ferent characters of metal, a suitable fluid for steel is produced from a mixture of nitric and muriatic acids. An appropriate alkaline wash is obtained by dissolving soda in water.

While different methods of applying the etching acid may suggest themselves, I have found that it may be done conveniently by means of a pad consisting of blotting paper or similar absorbent not readily affected by the etching fluid, backed up by a plate of glass or porcelain. By employing such a pad the fluid may be readily controlled, especially where it is desirable, as in my process, to

have the-fluid flow upward'through the sheet to the metallic surface instead of downward. In carrying out the step of applying the acid it is desirable to place a soaked pad face upward upon a table or other support and lower the metallic object onto it, the

coated and stamped sheet being between the metal and the pad with the clean surface toward the metal and the coated surface toward the pad. This causes the etching fluid to soak or travel upward, probably due to capillary attraction in the exposed portions of the paper sheet, and by proceeding thus a clear and sharp outline of the pattern wlll be produced. Furthermore, only so much of the fluid is removed from the pad,pract1- cally speaking, as will be drawn up through the exposed portions of the paper.

This .method'has several obvious advan tages. In the first place, it is extremely rapid compared with any process with which I am familiar.- When a resist is applied to the surface to be etched, it is necessary, of course, first to apply it, then produce. the a attern in. it, and then finally remove it. his requires considerable time. and skill and usually a waste of material. In my q process the metallic surface receives no coat-' ing whatever, and furthermore when a sheet has once been coated and the pattern traced or otherwise formed .in it, It may beused over and over 'again.' Another consideraace. In my process I contemplate and in practice use a sheet large enough to protect the entire object to be etched. Thus the sheet forms a shield for the work, although it will be understood that as the fumes are not as strong as the etching liquid, it isnot necessary ordinarily to apply the resistant substance to the entire sheet. As to rapidity, I have found that one of these completed etching sheets or matrices will last for several hundred impressions, and may be produced in little if any, greater time than it formerly took to print each object to be marked. I have also found that by weight ing the work pieces down upon the sheet and pads, for, example with a five pound weight when light objects are to be marked, and leaving them in this condition for a half minute or so, a single operator may attend to approximately eight pieces at a time, whereas by the ordinary process the work pieces usually have to be handled one at a time.

the coated side of the sheet and permitting the fluid to soak through'the exposed lines ing a matrix of'thin paper coated with a plastic substance resistant to the etching fluid and producing the pattern in said substance, deep enough -to expose the paper, laying face upward an absorbent pad charged with the etching fluid, and pressingthe work down on ,the pad with the matrix interposed, the clean sideof the paper being in contact with the work.

4. The etching process consisting in form ing a matrix of thin paper coated with a plastic substance resistant to the etching fluid and producing the pattern in said substance deep enough to expose the paper, laying face upward an absorbent pad charged with the etching fluid, and pressing the work down on the pad with the matrix interposed,

the clean side of the paper bein in-contact with the work, and the size 0 the sheet, being much greater than the area of the design whereby it forms a shield for the work to protect it from fumes rising from the In witness whereof, I have hereunto subscribed my name.

CARL e. OLSON. 

